Systems for inspecting semiconductor wafers or bare wafers have been proposed. See for example, U.S. Pat. No. 6,201,601. Systems such as those described in the above-referenced patent are useful for many applications, including the inspection of bare or unpatterned semiconductor wafers. Such systems typically scatter a laser beam from the wafer surface and collect the scattered radiation at a detector. The pattern of scattering can reveal defects in the wafer surface.
It is often desirable to use such sample inspection tools to inspect not only bare or unpatterned wafers but also rough surfaces, such as those found on the backside of a single-side polished (SSP) wafer. However, the extreme roughness of the surfaces involved often produces scattering noise that can be difficult to distinguish from signal scattered from defects. It is, therefore, desirable to provide an improved sample inspection system capable of distinguishing noise from defects on the backside of SSP wafers.